Catalyst for producing acrylonitrile

ABSTRACT

A fluidized-bed catalyst for producing acrylonitrile by the ammoxidation of propylene, which comprises a silica carrier and a composite having the following formula: 
     
       
         A a C c D d Na f Fe g Bi h M i Mo 12 O x   
       
     
     wherein A selected from the group consisting of potassium, rubidium, cesium, samarium, thallium and mixtures thereof; C is selected from the group consisting of phosphorus, arsenic, boron, antimony, chromium and mixtures thereof; D is selected from nickel, cobalt or mixtures thereof; M is selected from tungsten, vanadium or mixtures thereof. The catalyst of the present invention particularly suits the use under higher pressure and higher duties, and still maintains very high single-pass yield of acrylonitrile and a high ammonia conversion. This catalyst particularly suits the requirement for existing acrylonitrile plants to raise capacity. For new plants it can also reduce the investment on the catalyst and the pollution.

The present invention relates to a fluidized-bed catalyst for producingacrylonitrile by the ammoxidation of propylene.

The production of acrylonitrile by the ammoxidation has been developedfor more than 30 years and a balance has been approached between thecapacity of the acrylonitrile plants and the demand for acrylonitrile.Now the major development tendency of the production of acrylonitrilehas been transformed from the construction of new devices to thereformation of existing plants in order to reduce the consumption of thefeed stock and raise the capacity. By reformation of existing plants,change to effective catalysts and elimination of the bottleneck in theproduction process, it is possible to raise the capacity ofacrylonitrile by 50-80%, while the investment required is only 20-30% ofthat of a newly constructed device. The economic benefit is enormous.

Two problems will arise in the reformation of the plant: (1) thereaction pressure in the fluidized reactor will rise; (2) the catalystloading can not be too heavy. Therefore, the substitution catalystshould have a higher duty for propylene and the capability to endurehigher reaction pressures.

The reaction pressure of the fluidized-bed reactor is determined by aresistance of a serious of heat exchangers, towers and piping betweenthe outlet of the reactor and the top of the absorption tower. Anincrease in the capacity results in an appreciable increase in theamount of the effluent at the outlet of the reactor so that theaforesaid pressure drop is increased. Further, expanding of the heatconduction area in the heat exchangers contributes to additionalpressure drop. To meet the requirement of the environmental protection,the waste gas from the top of the absorption tower is not allowed topurge into the atmosphere, and should be passed to a furnace to burnoff. Thus, if a suction pump is not used, the pressure at the top of theabsorption tower must be raised. Because of the various reasonsmentioned above, the operation pressure of the prior reactor will be0.5-1.0 times higher than the designed value, i.e., reach above 0.08MPa.

The aforesaid second problem is the duty of the catalyst, i.e. WWH. Thedefinition of WWH is the tons of propylene treated per ton of catalystper hour. If the duty of the catalyst does not change, the catalystloading should increase accordingly when the feed to the reactorincreases. But the pipe of the cooling water is not high enough in theoriginal design, and therefore the fluidized height in the reactor mayexceed the height of the pipe of the cooling water. Moreover, the linearvelocity in operation also appreciably increases because the feed to thereactor increases. The combined effect of the two changes may cause therise of the temperature of the dilute phase in the reactor, the increasein the yield of carbon dioxide and the decrease in the selectivity toacrylonitrile. Therefore, higher WWH of the catalyst can prevent theaforesaid problems from accruing.

Theoretically, the ability of the catalyst to adsorb propylene should beenhanced by raising the WWH of the catalyst, but the theory that acertain element in a catalyst may enhance the ability to absorbpropylene is not available. A catalyst with the following compositionhas been disclosed in the literature CN 1021638C:

A_(a)B_(b)C_(c)Ni_(d)Co_(e)Na_(f)Fe_(g)Bi_(h)M_(i)Mo_(j)O_(x)

where A represents potassium, rubidium, cesium, samarium or thallium, Brepresents manganese, magnesium, strontium, calcium, barium, lanthanumor rare earth; C represents phosphorus, arsenic, boron, antimony orchromium; M represents tungsten or vanadium.

A higher single-pass yield of acrylonitrile can be obtained on the abovecatalyst, but the duty for propylene is lower and the single-pass yieldof acrylonitrile is greatly lowered under higher reaction pressures.Further research shows that components B and M in the above catalystcorrelate to the duty and the high-pressure performance of the catalyst.Although some elements of component B act for raising the single-passyield of acrylonitrile, they have negative effects on the duty and thehigh-pressure performance of the catalyst and unfavorable to thesuitability to operations at higher pressures and higher duties.Moreover, It has been defined in CN 1021638C that the sum of i and j inthe above catalyst composite is 12, i.e., a constant. This limitation iscanceled in the present invention because according to this limitation,an increase in component M will result in a decrease in component Mo,and this will affect the single-pass yield of acrylonitrile. Moreover,the literature does not report data on the ammonium conversion.Experiments have approved that the ammonia conversion is about 92-93%,which is relatively low.

The objects of the present invention are to provide a novel catalyst forproducing acrylonitrile, which is suitable for operations at higherreaction pressures and higher duties, maintains a high single-pass yieldof acrylonitrile and has a high ammonia conversion, to overcome theproblems of the catalyst of not being able to suit operations at higherreaction pressures and higher duties present in the above literature.

One object of the present invention is to provide a fluidized-bedcatalyst for producing acrylonitrile by the ammoxidation of propylene,which comprises a silica carrier and a composite having the followingformula:

A_(a)C_(c)D_(d)Na_(f)Fe_(g)Bi_(h)M_(i)Mo₁₂O_(x)

wherein A is at least one selected from the group consisting ofpotassium, rubidium, cesium, samarium, thallium and a mixture thereof; Cis at least one selected from the group consisting of phosphorus,arsenic, boron, antimony, chromium and a mixture thereof; D is selectedfrom nickel and cobalt or a mixture thereof; M is selected fromtungsten, vanadium or a mixture thereof;

a is 0.01-1.0, c is 0.01-2.0, d is 0.01-12, f is 0.2-0.7, g is 0.01-8, his 0.01-6, i is 0.01-9, x is the total number of the oxygen atom formeeting the requirement of the valence of the elements.

The carrier of the catalyst is silica, the content of which is 30-70% byweight.

Another object of the present invention is to provide a process forproducing acrylonitrile by the ammoxidation of propylene at higherreaction pressure and higher duties, wherein the catalysts as above-saidare used in a fluidized bed fulfilling the ammoxidation of propylene.

In the above technical solution, the preferred range of a is 0.03-0.4,the preferred range of c is 0.1-1.5, the preferred range of d is 0-8,the preferred range of f is 0.3-0.5, the preferred range of g is 0.1-4,the preferred range of h is 0.1-4, the preferred range of i is 0.1-6;the preferred range of the content of the silica carrier is 40-60% byweight.

There is no special requirement for the preparation procedure of thecatalyst of the present invention and the catalyst can be prepared bythe conventional procedure. First, various components are made into asolution, which is then made into a slurry by mixing with the carrier.The slurry is shaped into fine spheres via spray drying. Lastly, thefine spheres are calcined to obtain the catalyst. The preparation of theslurry is preferably made according to the procedure in CN 1005248C.

The chemicals for preparing the catalyst of the present invention are:

Component A is preferably the nitrate, hydroxide or salts that candecompose to oxides.

Phosphorus, arsenic, and boron of component C are preferably used in theform of their corresponding acids or ammonium salts. Chromium ispreferably used in the form of chromium (III) oxide, chromium nitrate,or a mixture thereof. Antimony may be used in the form of antimony (III)oxide, antimony (V) oxide; antimony halides or antimony sol that areable to hydrolyze to antimony oxides.

Components nickel, cobalt, iron, bismuth can be used in the form ofnitrates, oxides, or the salts that are able to decompose to oxides, butwater-soluble nitrates are preferable.

Tungsten in component M can be used in the form of ammonium tungstate ortungsten oxide, and vanadium in the form of ammonium metavanadate.

The molybdenum component in the catalyst can be used in the form ofmolybdenum oxide or ammonium molybdate.

Silica sol, silica gel or the mixture thereof can be used as thestarting material of silica that serves as a carrier. If silica sol isused, its quality must accord with the requirement of CN 1005248C.

The prepared slurry is sprayed drying after concentrated by heating to asolid content of 47-55%. The spray drier can be pressure type, dual-flowtype, or centrifugal rotary disc type, but the centrifugal type ispreferable, which can ensure that the ready catalyst has a gooddistribution of the particle size.

Calcination of the catalyst can be carried out in two stages:decomposition of the salts of various elements in the catalyst andhigh-temperature calcination. The temperature of the decomposition ispreferably 200-300° C., and the duration is 0.5-2 h. The calcinationtemperature is 500-800° C., preferably 550-650° C., and the calcinationduration is 20 min to 2 h. The aforesaid decomposition and calcinationcan be carried out separately in two furnaces, or in two zones of onefurnace, or simultaneously in a continuous rotary calcination furnace.During the decomposition and calcination of the catalyst, a certainamount of air should be introduced to prevent the catalyst fromexcessive reduction.

The standers of propylene, ammonia, and molecular oxygen required forproducing acrylonitrile by using the catalyst of the present inventionare the same as when other catalysts for the ammoxidation are used.Although the content of lower parafins in propylene has no effect on thereaction, from the economic viewpoint, the concentration of propylene ispreferably higher than 85% by mole. A fertilizer-grade ammonia can beused. As for molecular oxygen, pure oxygen, rich oxygen or air can beused from the technical viewpoint, but from the viewpoints of economyand safety, air is preferred.

The mole ratio of ammonia to propylene in the feed entering thefluidized-bed reactor is in the range of 0.8-1.5, preferably 1.0-1.3.The mole ratio of air to propylene is 8-10.5, preferably 9.0-9.8. If theoperation requires more air, this ratio can be increased to 11 withoutgreat effect on the reaction. However, from the viewpoint of safety, theexcessive oxygen in the reaction gas can not exceed 7% by volume,preferably does not exceed 4%.

When the catalyst of the present invention is used in a fluidized-bedreactor, the reaction temperature is 420-470° C., preferably 435-450° C.The catalyst of the present invention is a catalyst suitable foroperation under higher pressures and higher duties, and thus thereaction pressure in the production device can be higher than 0.08 MPa,such as 0.08-0.15 MPa. Even if the reaction pressure is lower than 0.08MPa, there is no unfavorable effect on the reaction and the single-passyield of acrylonitrile can further be raised.

The duty (WWH) of the catalyst of the present invention for propylene is0.06-0.15 h⁻¹, preferably 0.07-0.10 h⁻¹. Too low a duty not only wastesthe catalyst, but also increases the output of carbon dioxide anddecreases the selectivity of acrylonitrile. Too high a duty has nopractical significance because too little catalyst added makes the heattransfer area of the pipe of the cooling water in the catalyst layersmaller than that required for removal of the reaction heat and thusmakes the temperature out of control.

The prior recovering and refining process without any reformation can beused for processing the product produced with the catalyst of thepresent invention. That is, the unreacted ammonia is removed from theeffluent gas of the fluidized-bed reactor by passing through aneutralization tower and then all the organic compounds are absorbedwith low temperature water. Highly pure acrylonitrile product isobtained through extractive distillation, decyanation and dehydration ofthe absorbent liquid.

One of the characteristics of the catalyst of the present invention isthe high conversion of ammonia. Conventionally, it is not desired forthe acrylonitrile catalyst to have too high conversions of ammonia,because the rate of ammonia oxidation or combustion is higher than thatof the ammoxidation of propylene. If the ammonia conversion is too high,there is not enough ammonia to react with propylene so that a greatamount of oxidation products of propylene such as acrolein and acrylicacid and the like is formed, which will bring about difficulties in therecovering and refining of acrylonitrile. Therefore, the catalyst with ahigh ammonia conversion requires a high ammonia to propylene ratio. Thisis uneconomic. Even at high ammonia conversions, no great amount ofoxides is produced at a normal ammonia ratio because the catalyst of thepresent invention produces less oxidation products from propylene.

Because tungsten in component M favors the increase of the duty of thecatalyst and vanadium can improve the performance of the catalyst underhigher pressure, removal of some components that have negative effect onthe performance under higher pressures and higher duties and increase ofthe content of tungsten and vanadium provide the catalyst with goodperformance under a higher pressure (0.15 MPa) and a higher duty(WWH=0.15 h⁻¹), and still maintain the single-pass yield ofacrylonitrile at a level above 78%, and thereby good results areobtained.

The further description of the present invention will be given bellowwith examples.

EXAMPLE 1

8.5 g of the solution of potassium nitrate with a concentration of 20%,4.3 g of sodium nitrate, 8.2 g of the solution of cesium nitrate with aconcentration of 20% and 4.5 g of thallium nitrate are mixed anddissolved to make material (A).

43.7 g of ammonium tungstate is dissolved in 100 ml of 5% ammonia liquorand the resulted solution is mixed with 354.4 g of the solution ofammonium molybdate in 300 ml of hot water to obtain material (B).

135.1 g of iron nitrate is dissolved in 70 ml of water, thereto is added97.3 g of cobalt nitrate, 257.7 g of nickel nitrate and 81.1 g ofbismuth nitrate. This mixture is heated to dissolve the nitrates to givematerial (C).

Material (A) is mixed with 1250 g of sodium-free silica sol having aconcentration of 40% and stabilized by ammonia. While stirring, 12.3 gof phosphoric acid with a concentration of 20% and 8.4 g of chromium(VI) oxide is added to the mixture. After dissolution, materials (B) and(C) are added while stirring.

The resulted slurry is stirred and heated to concentrate to a solidcontent of about 50% and then sprayed drying with a centrifugal spraydrier. The formed fine powders of a sphere shape are calcined in arotary calcination furnace of 89 mm ID and 1700 mm length at 670° C. for1 h to yield a catalyst having the chemical composition of

Mo₁₂W_(1.0)Bi_(1.0)Fe_(2.0)Co_(2.0)Ni_(5.3)Cr_(0.5)P_(0.15)Na_(0.3)K_(0.1)Cs_(0.05)Tl_(0.1)+50%SiO₂

EXAMPLE 2

The catalyst having the following composition is prepared according tothe procedure in Example 1:

Mo₁₂W_(1.5)Bi_(1.0)Fe_(2.0)Co_(1.0)Ni_(6.3)Cr_(0.5)P_(0.15)Na_(0.3)K_(0.1)Cs_(0.05)Tl_(0.1)+50%SiO₂

where the amount of ammonium tungstate is 65.5 g, that of cobalt nitrateis 48.6 g, that of nickel nitrate is 306.4 g, with the others being thesame as in Example 1.

EXAMPLE 3

The catalyst having the following composition is prepared according tothe procedure in Example 1:

Mo₁₂W_(1.0)V_(0.2)Bi_(1.0)Fe_(2.0)Co_(2.0)Ni_(5.3)Cr_(0.5)P_(0.15)Na_(0.3)K_(0.1)Cs_(0.05)Tl_(0.1)+50%SiO₂

where the amount of ammonium metavanadate is 1.71 g, with the amount ofthe others being the same as in Example 1.

EXAMPLE 4

The catalyst having the following composition is prepared according tothe procedure in Example 1:

Mo₁₂W_(1.5)Bi_(1.5)Fe_(2.0)Co_(0.5)Ni_(6.5)Cr_(0.5)P_(0.15)Na_(0.3)K_(0.1)Cs_(0.1)Tl_(0.15)+50%SiO₂

where the amount of ammonium tungstate is 65.5 g, that of bismuthnitrate is 121.7 g, that of cobalt nitrate is 24.3 g, that of nickelnitrate is 316.1 g, that of cesium nitrate is 16.3 g of an aqueoussolution with a concentration of 20%, that of thallium nitrate is 6.7 g,with the amount of the others being the same as in Example 1.

EXAMPLE 5

The catalyst having the following composition is prepared according tothe procedure in Example 1:

Mo₁₂W_(2.0)Bi_(1.7)Fe_(2.0)Co_(0.5)Ni_(6.3)Cr_(0.5)P_(0.1)Na_(0.3)K_(0.1)Sm_(0.1)Tl_(0.2)+50%SiO₂

where the amount of ammonium tungstate is 87.6 g, that of bismuthnitrate is 137.9 g, that of cobalt nitrate is 24.3 g, that of nickelnitrate is 306.4 g, that of phosphoric acid is 8.2 g of an aqueoussolution of phosphoric acid with a concentration of 20%, that ofsamarium nitrate is 17.8 g of an aqueous solution with a concentrationof 20%, that of thallium nitrate is 9.0 g, with the amount of the othersbeing the same as in Example 1.

EXAMPLE 6

The catalyst having the following composition is prepared according tothe procedure in Example 1:

Mo₁₂W_(1.5)Bi_(1.5)Fe_(2.0)Co_(1.0)Ni_(6.0)Cr_(0.5)P_(0.25)Na_(0.3)K_(0.1)Rb_(0.1)Cs_(0.1)+50%SiO₂

where the amount of ammonium tungstate is 65.5 g, that of bismuthnitrate is 121.7 g, that of cobalt nitrate is 48.7 g, that of nickelnitrate is 291.8 g, that of phosphoric acid is 4.8 g of 85% phosphoricacid, that of cesium nitrate is 16.3 g of an aqueous solution with aconcentration of 20%, and the thallium nitrate in Example 1 is replacedby 12.3 g of an aqueous solution of rubidium nitrate with aconcentration of 20%, with the amount of the others being the same as inExample 1.

EXAMPLE 7

The catalyst having the following composition is prepared according tothe procedure in Example 1:

Mo₁₂W_(1.5)Bi_(1.0)Fe_(2.0)Co_(0.5)Ni_(7.5)Cr_(0.5)P_(0.25)Na_(0.3)K_(0.1)Rb_(0.1)Cs_(0.1)+50%SiO₂

where the amount of ammonium tungstate is 65.5 g, that of cobalt nitrateis 24.3 g, that of nickel nitrate is 364.8 g, that of phosphoric acid is4.8 g of an aqueous solution of phosphoric acid with a concentration of85%, that of cesium nitrate is 16.3 g of an aqueous solution with aconcentration of 20%, and thallium nitrate in Example 1 is replaced by12.3 g of an aqueous solution of rubidium nitrate with a concentrationof 20%, with the amount of the others being the same as in Example 1.

COMPARATIVE EXAMPLE 1

The catalyst having the composition of Example 1 in CN 1021638C isprepared using the procedure in Example 1, with the content of thesilica carrier being 50%.

Mo_(11.5)W_(0.5)Bi_(0.9)Fe_(1.8)Co_(4.0)Ni_(2.3)Mn_(1.0)Cr_(0.4)P_(0.25)Na_(0.3)Rb_(0.1)Cs_(0.5)

COMPARATIVE EXAMPLE 2

The catalyst having the composition of Example 3 in CN 1021638C isprepared using the procedure in Example 1, with the content of thesilica carrier being 50%.

Mo_(11.8)W_(0.2)Bi_(0.9)Fe_(1.8)Co_(4.0)Ni_(2.3)Mn_(1.0)Cr_(0.4)P_(0.15)B_(0.1)Na_(0.3)K_(0.1)Cs_(0.05)Tl_(0.1)

Evaluation tests of the catalyst activity. Evaluation tests of thecatalyst activity are carried in a fluidized catalyst of 38 mm ID. Thereaction pressure is regulated by a pressure regulator at the outlet ofthe reactor.

Evaluation result 1: Catalyst activity is tested under a higher reactionpressure and a higher duty for propylene. The catalyst loading is 400 g.The composition of the feed gas: propylene/ammonia/air=1:1.2:9.8,reaction temperature 440° C., reaction pressure 0.14 Mpa, WWH 0.085 h⁻¹.The results are as follows:

Single-pass yield (%) Conversion(%) Acrylo- Aceto- Hydrogen Acro-Acrylic Carbon Carbon Propy- Ammo- Catalyst nitrile nitrile cyanide leinacid monoxide dinoxide lene nia CE*1 77.7 2.5 1.9 0.5 1.4 3.3 9.5 96.892.1 CE*2 77.1 2.6 2.3 0.6 1.6 3.6 9.3 97.1 91.8 Example 1 79.7 2.8 1.90.5 1.5 3.1 8.1 97.5 96.5 Example 2 79.4 3.1 1.1 0.5 1.5 2.7 9.4 97.697.1 Example 3 79.5 2.6 2.1 0.5 1.5 3.3 8.1 97.5 97.0 Example 4 79.2 2.72.6 0.8 1.5 3.0 7.5 97.3 96.8 Example 5 79.5 2.8 2.2 0.4 1.3 3.2 8.798.1 97.3 Example 6 79.5 3.4 1.0 0.5 1.5 2.5 9.0 97.6 97.1 Example 779.6 2.5 1.9 0.4 1.5 3.2 8.7 97.9 96.6 *Comparative example

Evaluation result 2: Catalyst activity is tested under a normal reactionpressure and a normal duty for propylene. The catalyst loading is 550 g.The composition of the feed gas: propylene/ammonia/air=1:1.2:9.8,reaction temperature 440° C., reaction pressure 0.082 MPa, WWH 0.045h⁻¹. The results are as follows:

Single-pass yield (%) Conversion(%) Acrylo- Aceto- Hydrogen Acro-Acrylic Carbon Carbon Propy- Ammo- Catalyst nitrile nitrile cyanide leinacid monoxide dioxide lene nia CE*1 79.3 2.8 1.6 0.2 1.0 3.8 9.2 98.193.5 CE*2 79.5 2.9 1.4 0.3 1.1 3.5 8.9 96.7 93.0 Example 1 80.6 2.9 2.20.5 1.6 3.3 8.0 99.0 97.0 Example 2 80.5 3.0 1.6 0.2 1.8 3.1 9.2 99.497.4 Example 3 80.4 2.7 2.1 0.5 1.8 3.5 8.1 99.0 97.5 Example 4 81.1 3.30.9 0.2 1.6 2.6 8.6 99.1 97.1 Example 5 81.4 3.7 1.0 0.1 1.7 2.8 8.999.4 97.8 Example 6 80.8 3.2 1.2 0.3 1.7 2.7 9.0 98.9 97.5 Example 780.7 3.2 1.4 0.5 1.7 2.7 8.9 99.2 97.2 *Comparative example

Evaluation result 3: The activity is tested with the catalyst of Example1 of the present invention under different reaction pressures. Thecatalyst loading is 400 g. The composition of the feed gas:propylene/ammonia/air=1:1.2:9.8, reaction temperature 440° C., WWH 0.085h⁻¹. The results are as follows:

Reaction Single-pass yield (%) Conversion(%) pressure Acrylo- Aceto-Hydrogen Acro- Acrylic Carbon Carbon Propy- Ammo- (MPa) nitrile nitrilecyanide lein acid monoxide dioxide lene nia 0.08 79.6 2.1 2.3 2.0 2.12.5 7.1 97.8 97.5 0.09 79.7 2.4 1.7 1.7 2.2 2.5 7.2 97.4 97.0 0.10 80.12.1 2.7 1.1 1.6 3.2 7.5 98.3 97.1 0.11 79.7 2.3 2.7 0.9 1.7 3.2 7.6 98.096.9 0.12 79.4 2.7 2.0 0.9 1.7 2.9 7.8 97.3 96.7 0.13 79.4 2.6 2.5 0.51.6 3.2 7.7 97.5 96.5 0.14 79.7 2.8 1.9 0.5 1.5 3.1 8.1 97.5 96.5 0.1578.2 3.2 2.5 0.5 1.6 3.4 7.8 97.1 96.3

The above tests show that, compared with the prior art CN 1021638C, thecatalyst of the present invention increases the single-pass yield ofacrylonitrile by 1.0-1.5%, and increases the conversion of ammonia by3-4% under a normal pressure and a normal duty, and increases thesingle-pass yield of acrylonitrile by 1.5-2.0%, and increases theconversion of ammonia by 4-5% under a higher pressure and a higher duty.Moreover, the single-pass yield of acrylonitrile on the catalyst of thepresent invention is lowered to a less extent than the prior artcatalyst when the reaction pressure is raised.

What is claimed is:
 1. A fluidized-bed catalyst for producingacrylonitrile by the ammoxidation of propylene, which consists of asilica carrier and a composite having the following formula:A_(a)C_(c)D_(d)Na_(f)Fe_(g)Bi_(h)M_(i)Mo₁₂O_(x) wherein A is selectedfrom the group consisting of potassium, rubidium, cesium, samarium,thallium and mixtures thereof; C is selected from the group consistingof phosphorus, arsenic, boron, antimony, chromium and mixtures thereof;D is nickel, cobalt or mixtures thereof; M is vanadium or a mixture ofvanadium and tungsten; a is 0.01-1.0, c is 0.01-2.0, d is 0.01-12, f is0.2-0.7, g is 0.01-8, h is 0.01-6, i is 0.01-9, x is the total number ofthe oxygen atom for meeting the requirement of the valence of theelements; and wherein the content of the carrier in the catalyst is30-70% by weight.
 2. A fluidized-bed catalyst for producingacrylonitrile by the ammoxidation of propylene according to claim 1,wherein a is 0.03-0.4, c is 0.1-1.5, d is 0.1-0.8, f is 0.3-0.5, g is0.1-4, h is 0.1-4, and i is 0.1-6.
 3. A fluidized-bed catalyst forproducing acrylonitrile by the ammoxidation of propylene according toclaim 1, wherein the content of the silica carrier in the catalyst is40-60% by weight.
 4. A process for producing acrylonitrile by theammoxidation of propylene at higher reaction pressure and higher dutiesusing the catalysts according to anyone of claims 1-3, wherein thereaction pressures are in the range of 0.08-0.15 MPa and the duties ofpropylene (WWH) are in the range of 0.06-0.15 h⁻¹.